Up-conversion FRET from Er3+/Yb3+:NaYF4 Nanophosphor to CdSe Quantum Dots

Forster resonance energy transfer (FRET) between nanoparticles or up-conversion lanthanide phosphor is donors and quantum dots as acceptors is demonstrated. Fluoride (NaYF4) nanocrystals (ca. 30 nm size) codoped with the Er3+. and Yb3+ ions were synthesized with a high-pressure solvothermal microwave assisted technique and dispersed in organic solvent. Up-converted luminescence from the rare-earth ions doped into fluoride nanomatrix was achieved with optical pumping in NIR (976 nm) region. The green erbium upconversion emission at 540 nm is efficiently quenched by quantum dots (QDs) leading to color change of the mixture for different relative concentrations. Simultaneously, orange emission From quantum dots appears due to energy transfer from Er3+/Yb3+:NPs donors to QDs acceptors. The concomitant decrease of. the average lifetime of donor emission at 540 nm (from similar to 153 to similar to 130 mu s) indicates that the excitation of CdSe QDs occurs not only through reabsorption but also through Forster Resonance Energy Transfer. Acceptor luminescence lifetime mimics that of the donor and reaches hundreds of microseconds, The Forster radius (R-0) was calculated to be short (similar to 15 angstrom), mostly clue to low quantum yield of the multilevel emitting donor. This short-range interaction proves that in our system the FRET occurs mostly through Er3+ ions proximate to the surface, resulting in efficiency of energy transfer equal to eta = 14.8%.